1. Field of the Invention
The present invention concerns a friction clutch, notably for a motor vehicle, and relates more particularly to a clutch equipped with a device for compensating for the wear due notably to the wear on at least one friction lining, the said device, referred to hereinafter as a wear take-up device, operating gradually as the wear occurs on the said lining or linings.
It relates to the friction clutch mechanisms which such a clutch has.
2. Description of the Related Art
A conventional friction clutch generally has a reaction plate forming part of an engine flywheel, possibly in two parts in order to form a damping flywheel or a flexible flywheel, fixed with respect to rotation to a first shaft, usually a driving shaft such as the crankshaft of the internal combustion engine, and supporting, through its external periphery, a cover to which at least one pressure plate is attached with axial mobility.
The pressure plate is fixed with respect to rotation to the cover and the reaction plate whilst being able to move axially under the action of axially acting engagement means controlled by disengagement means. The disengagement means can consist of helical springs, or two Belleville washers mounted in series, subject to the action of disengagement levers forming the disengaging means.
Generally, the engaging and disengaging means form part of the same piece, for example a metallic diaphragm bearing on the cover; the diaphragm can be mounted in series or in parallel with a Belleville washer in order to provide assistance for the disengagement force.
A friction disc, carrying friction linings at its external periphery, fixed with respect to rotation to a shaft, usually a driven shaft such as the gearbox input shaft, is interposed between the pressure plate and the reaction plate so as to be gripped between them when the clutch is in the engagement position in order to transmit the torque from the driving shaft to the driven shaft.
Conventionally, the friction linings are mounted on an axially elastic support coupled rigidly or elastically to a hub fixed with respect to rotation to the driven shaft. By virtue of this arrangement the friction disc assists the diaphragm during the operation of disengaging the clutch. As a variant, the support is rigid whilst for example being embedded at its external periphery in a single friction lining.
Conventionally, the engaging means, the cover and the pressure plate form part of a unitary assembly referred to as a friction clutch mechanism.
The engaging means control the axial movement of the pressure plate when they are actuated by a clutch release bearing by means of disengaging means.
The clutch release bearing can be controlled mechanically, hydraulically or electrically. The control can be of the manual, automatic or semi-automatic type.
During the service life of such a clutch, the friction lining or linings, as well as the counter-materials, pressure plate and reaction plate, wear, which causes a variation in the position of the pressure plate and that of the axially acting engaging means and of the clutch release bearing, resulting in a variation in the clamping force between the friction disc on the one hand and the pressure and reaction plates on the other hand, because of the changes in the working conditions of the engaging means, and the force necessary for disengaging is affected thereby. By providing such a clutch with a wear take-up device, these drawbacks are avoided, the engaging means, and the clutch release bearing, usually in continuous abutment on the disengaging means, occupying the same position when the clutch is in the engagement position so that the axial dimension of the clutch is reduced.
In the document FR 96 11297 filed on Sep. 17, 1996 and published under the number 2 753 503, the wear take-up device has, in FIGS. 21 to 26, a unit comprising, in a unitary fashion, a U-shaped support with a web and two lateral wings each provided with a hole for supporting at least one shaft carrying a worm, a ratchet wheel and a helical spring. The support also carries an elastic member provided, on the one hand, with a control tongue and on the other hand with a non-return catch.
The control tongue is able to be maneuvered by an actuator forming part of the engaging means of the clutch and cooperates, as well as the catch, with the teeth on the ratchet wheel.
The worm cooperates with the teeth of a set of teeth fixed with respect to rotation to the ramp means placed between the abutment means of the engaging means and the pressure plate. The worm cooperates with the set of teeth and with means of driving in rotation, comprising the helical spring forming a take-up spring, which are made operational by the wear on the friction linings when the clutch is engaged. The worm is mounted tangentially with respect to its associated set of teeth.
It is desirable to improve the cooperation of the worm with the set of teeth.
The object of the present invention is to meet this requirement simply and economically.
According to the invention a clutch mechanism of the type indicated above is characterised in that the holes in the wings are offset axially with respect to each other.